It has been known that corrosion of amorphous carbon catalyst supports and metal catalyst, which occurs during startup and shutdown of polymer electrolyte membrane (PEM) fuel cells, results in a permanent decay of fuel cell performance. It has also been known that the corrosion is due to a reverse current situation in which the cathode potential may be well in excess of one volt higher than the potential of a standard hydrogen electrode. It is believed that this is caused by both hydrogen and air being present at different locations within the anode flow field. During a shutdown period, where no inert gas purge is used, air will slowly, uniformly fill both the anode and cathode flow field of the fuel cell. During startup, hydrogen is fed to the anode flow field which results in the inlet to the anode flow field being primarily hydrogen while the exit of the anode flow field is primarily air. An electrochemical reaction occurs between the fuel rich zone in the anode flow field and the oxygen rich zone in the anode flow field that causes the potential of the anode in the oxygen rich zone to increase to the air open-circuit potential. This in turn raises the potential of the cathode, opposite to the air rich zone on the anode, to a potential of 1.4-1.8 volts versus a standard hydrogen electrode. This potential causes the carbon based catalyst support to corrode and results in decreased cell performance. In automotive applications, that may experience 50,000-100,000 startup/shutdown cycles, this results in catastrophic performance loss. Heretofore, solutions to this problem include stabilizing the fuel cell stack by purging the anode flow fields with an inert gas, such as nitrogen, and maintaining an auxiliary load across the fuel cell stack during the shutdown and startup processes.
In commonly owned, copending U.S. patent application Ser. No. 09/742,481, filed Dec. 20, 2000, it is shown that as the fresh hydrogen-containing fuel flows through the anode flow field upon startup, to displace the air therein, the corrosion of the platinum catalyst and catalyst support occurs as the hydrogen/air interface moves through the anode flow field. The extent of corrosion is mitigated by rapidly purging the air with hydrogen during startup of the fuel cell. In a similar fashion, it is known that as purge air is passed through the anode upon shut-down, there is a hydrogen/oxygen interaction, which creates a potential safety hazard and may cause undesirably large voltage excursions in the cells, as described in commonly owned, copending U.S. patent application Ser. No. 09/742,497, filed Dec. 20, 2000.